K-Ar ages of plutonic rocks in the Lassiter Coast area, Antarctica

Numerous middle Cretaceous stocks and small batholiths intruded Middle and Upper Jurassic sedimentary and volcanic rocks in the Lassiter Coast area of the southern Antarctic Peninsula. To establish the age of the quartz diorite and granodiorite plutonic events, five plutons were dated by the K-Ar method. The results indicate a timespan of about 20 m.y. for the emplacement of the plutons and a minimum age of 120 m.y. for the deformation of the sedimentary (Latady Formation) and volcanic rocks. Three of the more silicic plutons have concordant biotite and hornblende ages of 100 and 106 m.y.; two discordant ages of about 118 m.y. were obtained on the more mafic plutons. Petrographically, chemically, and geochronologically, the plutons of the southern to central Lassiter Coast are similar to the calc-alkaline suite of igneous rocks of the Andes of Patagonia, the Antarctic Peninsula, and eastern Ellsworth Land.